I'm not so sure about having a full blown wiki. It seems like an administrative nightmare to keep content legal, not spam, and concise. I can see the benefits in the forums for such a thing, because it would be nice to have the first post be updatable with information as the thread gets long. Instead of a full wiki, I would look at a system like slickdeals.net where forum threads can have the original post turn into wiki format. Basically the most common use case I can think of is where there is lots of DATA, not opinion, being compiled by users. Trying to make wiki for brand reviews is probably going to be fruitless as some people will inevitably start deleting conflicting information with their own beliefs.